var banner = new Array();

banner[0]='http://i39.tinypic.com/98gjza.jpg';
banner[1]='http://i42.tinypic.com/smvo1t.jpg';
banner[2]='http://i45.tinypic.com/11lsm88.jpg';

document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];